The ultimate goal of this project is to identify molecular mechanisms of pathogenesis and potential therapeutic targets that are common to Spinocerebellar ataxias (SCAs). These are a group ~30 genetically heterogeneous neurodegenerative disorders that share neuropathological and clinical features such as atrophy of the cerebellum and loss of motor coordination and balance. Recent data points to unsuspected links among inherited ataxias. First, a proteinprotein- interaction network for inherited ataxias revealed that many ataxia-causing proteins share interacting partners. Second, dAtaxin-2 (an orthologue of the protein responsible for SCA2) is a major modifier of Ataxin-1[82Q]-induced neurotoxicity in a Drosophila model of SCA1. Together, these observations suggest that SCAs, and perhaps other inherited ataxias may share molecular mechanisms of pathogenesis in addition to similar neuropathology and clinical features. This hypothesis predicts that SCAs have common genetic modifiers and potential therapeutic targets that remain unknown. Testing this hypothesis requires a thorough comparison of genetic modifiers and mechanisms of pathogenesis among different inherited ataxias. A genetic approach will be employed to identify modifiers of neurotoxicity caused by expanded Ataxin-1, Ataxin-2 and Ataxin-7, the proteins responsible for SCA1, SCA2 an SCA7. The work proposed here will address the following specific aims: 1) To investigate the molecular mechanisms by which partial loss of dAtaxin-2 function suppresses Ataxin-1[82Q]-induced neurodegeneration. 2) To screen the ataxia interactome for genetic modifiers of Ataxin-1[82Q]-induced neurotoxicity. 3) To test the Ataxin-1[82Q] genetic modifiers and the ataxia interactome in Drosophila models of SCA2 and SCA7. 4) To investigate selected genetic modifiers that are common to the Drosophila SCA models. These comparative studies are impractical with mammalian models, but feasible using Drosophila. The suppressors of neurodegeneration identified as a result of this work may directly point to specific therapeutic targets. These basic studies are prerequisite to developing therapies for these neurodegenerative disorders for which there are no effective treatments.